linux-kernel - Re: [PATCH] timer: Preserve higher bits of expiration on index calculation

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Message-ID: <87r1tbtu5o.fsf@nanos.tec.linutronix.de>
Date:   Thu, 16 Jul 2020 16:24:19 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH] timer: Preserve higher bits of expiration on index calculation

Frederic Weisbecker <frederic@...nel.org> writes:
> Subject: [PATCH] timer: Preserve higher bits of expiration on index
>  calculation
>
> The higher bits of the timer expiration are cropped while calling
> calc_index() due to the implicit cast from unsigned long to unsigned int.
>
> This loss shouldn't have consequences on the current code since all the
> computation to calculate the index is done on the lower 32 bits.
>
> However we are preparing to return the actual bucket expiration from
> calc_index() in order to properly fix base->next_expiry updates.
> Preserving the higher bits is a requirement to achieve that.

Nice catch!